For example, a direction indication device as illustrated in FIG. 6 is known as a direction indication device for a motorcycle. The direction indication device includes a diode D101, a capacitor C101, a direction indication switch SW, a left-side direction indication lamp 102L, a right-side direction indication lamp 102R, an internal power source 103, an oscillator 104a, a buffer 104b, an N-type MOS transistor NM101, a comparator COMP101 for wire disconnection detection, and a current detection resistor R101. The left-side direction indication lamp 102L has a left-front-side bulb 102LF and a left-rear-side bulb 102LR which are connected to each other in parallel. The right-side direction indication lamp 102R has a right-front-side bulb 102RF and a right-rear-side bulb 102RR which are connected to each other in parallel. The diode D101 and the capacitor C101 function as a bootstrap circuit.
Operation of the direction indication device will be described. For example, when the direction indication switch SW is ON to the side of an L terminal, a terminal on the negative side of the capacitor C101 is grounded via the bulbs 102LF and 102 LR. Thus, current from a battery B flows through the capacitor C101 via the diode D101, and thus the capacitor C101 is charged. Accordingly, the internal power source 103, the oscillator 104a, a buffer 104b and the comparator COMP101, to which an internal power supply voltage Vcc is supplied from a terminal on the positive side of the capacitor C101, and to which a reference voltage VS is supplied from the terminal on the negative side, are activated. The internal power source 103 generates a voltage V101 or the like supplied to the comparator COMP101.
The activated oscillator 104a generates an oscillation pulse signal. The buffer 104b outputs the pulse signal by buffering the oscillation pulse signal. The N-type MOS transistor NM101 causes a drive current, a magnitude of the drive current corresponding to the amplitude of a pulse signal supplied to a gate, to flow from a drain to which the power supply voltage VDD is supplied, to a source. The drive current flows through the bulbs 102LF and 102LR of the direction indication lamp 102L via the current detection resistance R101 and the direction indication switch SW. Accordingly, the direction indication lamp 102L blinks at a period of the oscillation pulse signal.
In the direction indication device, in a case where any one of the front-side and rear-side bulbs 102 LF and 102 RF is wire-disconnected, the drive current is reduced. Consequently, the comparator COMP101 detecting an increase in the power supply voltage VDD resulting from a decrease in the drive current controls the oscillator 104a and thus causes a period of the oscillation pulse signal to be changed. Accordingly, since a blinking period of the direction indication lamp 102L is changed, the wire disconnection of the bulb may be reported to a user or the like.
The direction indication device as disclosed in JP 1-90831 A is also known as a device similar to this direction indication device.
Incidentally, it is desired that an LED element is used as the direction indication lamps 102L and 102R of the direction indication device, instead of a bulb. In this case, in order to extend a lifetime of an LED element and stabilize an amount of light, the LED element is preferably controlled so that constant current flows through the LED element.
However, in a case where the constant current control is performed, drive current remains unchanged and the wire disconnection detection may not be performed by monitoring a change in the drive current, even though any one of the front-side and rear-side LED elements is disconnected, because the control is performed so that twice the current flows through the remaining normal LED element to make constant current flow. Furthermore, when twice the current flows through the remaining LED element at the time of one-side wire disconnection, the lifetime of the LED element is notably shortened.